Malignant tumors shed cells, which migrate to new tissues and create secondary tumors. The process of generating secondary tumors is called metastasis and is a complex process in which tumor cells colonize sites distant from the primary tumor. Liotta ((1986) Cancer Res. 46, 1-7) has proposed a three-step hypothesis for the process of metastasis: The first step is tumor cell attachment via cell surface receptors. The anchored tumor cell next secretes hydrolytic enzymes or induces host cells to secrete enzymes, which can degrade the matrix locally. Matrix lysis most likely takes place in a highly localized region close to the tumor cell surface. The third step is tumor cell locomotion into the region of the matrix modified by proteolysis. Thus, invasion of the matrix is not merely due to passive growth pressure but requires active biochemical mechanisms. Degradation of the surrounding normal tissue is a central feature of invasiveness of malignant tumors. The process of metastasis formation depends on the invasiveness of tumor cells. It would, therefore, be useful to develop drugs, which inhibit invasiveness and therewith prevent metastasis of primary tumors.
Recently, research has been focused on identifying specific proteins involved in metastasis, which can be used as a basis for better diagnostic or improved therapeutic strategies. A protein that has been identified as a molecular chaperone molecule and that is essential for the stability and function of several oncogenic proteins is heat shock protein 90 (Hsp90). This name is a generic term used to describe two isoforms termed Hsp90α and β. The structure and the function of the isoforms of Hsp90 is described in Csermely et al.: Pharmacol. Ther. Vol. 79, 1998, No. 2, The 90-kDa Molecular Chaperone Family: Structure, Function, and Clinical Applications. A Comprehensive Review, p. 131, p. 146. Hsp90 is one of the most abundant chaperones in the cytosol of eukaryotic cells and constitutes approximately 1-2% of all proteins in the cell. The intracellular functions of Hsp90 include stabilization of proteins (steroid receptors) and maturation of proteins such as kinases and other signalling proteins. Hsp90 has been implicated, however, in a wide variety of functions including evolutionary stability of mutated proteins, cytoskeletal rearrangements, nuclear transport, cell proliferation and apoptosis, protein degradation, antigen presentation and lipopolysaccharide recognition. Being very abundant in the cell Hsp90 has also been linked to many diseases, from cancer to autoimmune disease to cardiovascular disease. For example, a monoclonal antibody to the immunodominant LKVIRK (SEQ ID NO: 55) epitope of Hsp90 showed therapeutic activity in a treatment against fungal infection and was used in a clinical trial by the firm Neutec under the trade name Mycogrip™.
It has also been shown that Hsp90 is secreted from the cells in response to stress (Liao et al. (2000) J. Biol. Chem. 275, 189-96), but no known function has been associated with this secretion.
While Hsp90 has well-established functions intracellularly, reports of extracellular occurrence and its function are scarce. Hsp90 has been found to be an effective antigenic peptide presenter to receptors on antigen presenting cells. It has also been found to be one of four proteins associated in lipid rafts on the extracellular surface of cells, which bind to lipopolysaccharide and initiate intracellular responses (Triantafilou et al. (2002) Trends in Immunology 23, 301-4). Hsp90 has also been found overexpressed on the surface of some tumor cells: microcitomas, melanoma, and hepatoma cell lines (Ferrarini et al. (1992) Int. J. Cancer 51, 613-19). It has been hypothesized that expression of Hsp90 on the surface of these cell lines is connected to antigen presentation, but clear evidence is not yet available.
Hsp90 is also currently being assessed as an intracellular target in anti cancer drug development, due to its involvement in regulating several signalling pathways that are of importance in driving the phenotype of a tumor Inhibition of Hsp90 function has been shown to cause selective degradation of signalling protein involved in cell proliferation, cell cycle regulation and apoptosis. Several known antibiotics (e.g. geldanamycin, radicicol, and coumermycin A1) have been shown recently to be inhibitors of Hsp90 and are described in WO 00/53169. In this document a method of inhibiting binding of a chaperone protein with its client is proposed, wherein the method proposes contacting a chaperone protein with coumarin or a coumarin derivative. However, the teaching of WO 00/53169 is directed merely to the inhibition of intercellular Hsp90 protein.
Inhibitors such as the geldanamycin analogue 17-AAG are already being tested in clinical trials but there are concerns about toxicity resulting from non-specific inhibition of the protein across all cellular compartments (Dunn (2002) J. Natl. Cancer Inst 94, 1194-5). Furthermore, the lack of understanding of the interaction of Hsp90 with client proteins in various cell signalling processes bears potential risks of inhibiting intracellular Hsp90 with toxic inhibitors.
The determination of the physiological role of a protein is a prerequisite for deciding whether interference with this protein function might be a possible avenue for the treatment of disease or not. It must be kept in mind that in a physiological setting, i.e. in a naturally occurring tumor cell of a patient, Hsp90 acts together with other proteins, which can modulate and interfere with each other. It is the functional interplay between Hsp90 and interacting proteins that determines its physiological role.
Hsp90 has also been reported to act as a molecular chaperone for transmembrane protein transport in the nucleus (Schlatter et al. (2002) Biochem. J. 362, 675-84), and has been implicated in drug efflux in leukemia, lung and ovarian carcinoma cells (Rappa et al (2002) Oncol. Res. 12, 113-9 and Rappa, et al (2000) Anticancer Drug Des 15, 127-34).
The present invention demonstrates for the first time that the inhibition of extracellular Hsp90 leads to a reduction of the invasiveness of the tumor cells. The present invention shows a novel avenue to inhibit extracellular Hsp90 whereby side effects associated with attacking the intracellular Hsp90 can be prevented.
The present invention also shows an interrelationship between Hsp90 inhibition and the secretion of matrix metalloproteases (MMPs). MMPs act in invasion by digesting surrounding extracellular matrix to allow cells to migrate through dense tissues. Our results showed that Hsp90 is critical for invasion of cancer cells by increasing secretion or activity of MMPs, when overexpressed in fibrosarcoma cells. We further showed that Hsp90-dependent invasion can be inhibited by using the molecules of the invention.
The present invention relates to the use of molecules interfering with the function of extracellular Hsp90 on tumor cells for the treatment of specific cancers. Compounds, compositions and methods are provided that are useful for reducing or inhibiting the invasiveness and/or the metastatic potential of specific tumor cells. Furthermore, a method is provided that allows to determine whether a tumor cell depends on functional extracellular Hsp90 for its invasiveness and/or metastatic potential.